Surface acoustic wave device for sensing a touch-position

ABSTRACT

A surface acoustic wave position-sensing device comprising two surface acoustic wave transducing units, a nonpiezoelectric plate and a controlling system connected with the units. Each unit consists of two piezoelectric substrates, a first group of interdigital transducers (IDTs) and a second group of interdigital transducers (IDTs). The second group of the IDTs is placed such that the finger direction thereof is slanting to that of the first group of the IDTs by an angle α. The thickness of each piezoelectric substrate is smaller than an interdigital periodicity of the IDTs. The thickness of the nonpiezoelectric plate is larger than three times the interdigital periodicity. When an electric signal is applied to the first group of the IDTs, a SAW is excited in one of the piezoelectric substrates and transmitted to the other of the piezoelectric substrates through the upper end surface of the nonpiezoelectric plate. The controlling system senses a touch with a finger on the upper end surface of the nonpiezoelectric plate by the generation of the electric signal at one of the second group IDTs.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface acoustic wave device forsensing a touch-position on a nonpiezoelectric plate having two surfaceacoustic wave transducing units.

2. Description of the Prior Art

An ultrasonic form of conventional touch panels has a nonpiezoelectricplate under acoustic vibration, which is decreased or disappeared whentouching on the nonpiezoelectric plate. Conventional methods forexciting the acoustic vibration on a nonpiezoelectric plate generallyinclude a wedge-shaped transducer with a bulk wave vibrator forvibrating a nonpiezoelectric plate indirectly, or a piezoelectric thinfilm transducer for vibrating a nonpiezoelectric plate directly. Thewedge-shaped transducer is mainly used for a non-destructive evaluationby ultrasound under a comparative low frequency operation alone becauseof the difficulty on manufacturing accuracy of the wedge angle and soon. The piezoelectric thin film transducer consists of anonpiezoelectric plate, a piezoelectric thin film mounted on thenonpiezoelectric plate and made from ZnO and others, and interdigitaltransducers exciting the acoustic vibration on the nonpiezoelectricplate. Because of various transmission characteristics of theinterdigital transducers with various structures, the piezoelectric thinfilm transducer is used as a high frequency device, however hasoperation frequencies limited to the UHF and VHF bands, and has someproblems on manufacturing and mass production. In addition,conventional-type transducers make use of decreasing or disappearance ofoutput electric signal in accordance with decreasing or disappearance ofan acoustic wave on the nonpiezoelectric plate by touching thereon,causing a high voltage operation with a high power consumption, and alarge-scale circuit with a complicated structure.

Thus, it is difficult for conventional touch panels to realize a quickresponse-time, a low voltage operation and a low power consumption, anaccurate detection of a minute touch-position, and a small-sized circuitwith a simple structure. Moreover, there are some problems onmanufacturing, mass production and operation frequencies.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a surface acoustic waveposition-sensing device capable of specifying a minute touch-position ona nonpiezoelectric substrate with a high sensitivity and a quickresponse time.

Another object of the present invention is to provide a surface acousticwave position-sensing device excellent in manufacturing andmass-production.

A still other object of the present invention is to provide a surfaceacoustic wave position-sensing device operating under low powerconsumption with low voltage.

A still further object of the present invention is to provide a surfaceacoustic wave position-sensing device having a small-sized circuit witha simple structure which is very light in weight.

According to one aspect of the present invention there is provided asurface acoustic wave position-sensing device comprising two surfaceacoustic wave transducing units X and Y, a nonpiezoelectric plate havingan upper- and a lower end surfaces running perpendicular to thethickness direction thereof, and a controlling system connected with thesurface acoustic wave transducing units X and Y. Each surface acousticwave transducing unit consists of a piezoelectric substrate P_(T) havingtwo end surfaces running perpendicular to the direction of the thicknessd thereof, a piezoelectric substrate P_(R) having two end surfacesrunning perpendicular to the direction of the thickness d thereof, aninput interdigital transducer T_(o) formed on one end surface of thepiezoelectric substrate P_(T), N input interdigital transducers T_(i)(i=1, 2, . . . , N) formed on the one end surface of the piezoelectricsubstrate P_(T), an output interdigital transducer R_(o) opposed to theinterdigital transducer T_(o) and formed on one end surface of thepiezoelectric substrate P_(R), and at least two output interdigitaltransducers R_(i1) and R_(i2) (i=1, 2, . . . , N) opposed to eachinterdigital transducer T_(i) and formed on the one end surface of thepiezoelectric substrate P_(R). The interdigital transducer R_(o) isplaced such that the finger direction of the interdigital transducerR_(o) runs parallel with that of the interdigital transducer T_(o). Thethickness d of the piezoelectric substrates P_(T) and P_(R) is smallerthan an interdigital periodicity P of the interdigital transducersT_(o), T_(i) and R_(o). The thickness of the nonpiezoelectric plate islarger than three times the interdigital periodicity P. Each of theinterdigital transducers R_(i1) and R_(i2) is placed such that thefinger direction thereof is slanting to that of the interdigitaltransducer T_(i) by an angle α. An interdigital periodicity P_(N) alongthe vertical direction to the finger direction of the interdigitaltransducers R_(i1) and R_(i2) is equal to the product of theinterdigital periodicity P and cos α. The sum of an overlap length L_(P)along the finger direction of the interdigital transducer R_(i1) andthat of the interdigital transducer R_(i2) is approximately equal to theproduct of an overlap length L of the interdigital transducer T_(i) andsec α. The piezoelectric substrates P_(T) and P_(R) are mounted on theupper end surface of the nonpiezoelectric plate.

When an electric signal with a frequency approximately corresponding tothe interdigital periodicity P is applied to each of the interdigitaltransducers T_(o) and T_(i), a surface acoustic wave of the first modeand the higher order modes is excited in the piezoelectric substrateP_(T) and transmitted to the piezoelectric substrate P_(R) through theupper end surface of the nonpiezoelectric plate. The phase velocity ofthe surface acoustic wave of the first mode and the higher order modesis approximately equal to the phase velocity of the Rayleigh wavetraveling on the nonpiezoelectric plate alone. The surface acoustic waveexcited by the interdigital transducer T_(o) is transduced to anelectric signal with a phase θ_(base), and delivered at the interdigitaltransducer R_(o). The surface acoustic wave excited by each interdigitaltransducer T_(i) is transduced to electric signals E_(j) (j=1, 2, . . ., X) with phases θ_(j) (j=1, 2, . . . , X), by each of the interdigitaltransducers R_(i1) and R_(i2), the phases θ_(j) corresponding topositions F_(j) (j=1, 2, . . . , X) on the upper end surface of thenonpiezoelectric plate, each electric signal E_(j) having a frequencyapproximately corresponding to the interdigital periodicity P. The totalphase Σθ_(j) made by the phases θ_(j) is zero, and the total electricsignal ΣE_(j) made by the electric signals E_(j) is also zero and notable to be detected at each of the interdigital transducers R_(i1) andR_(i2). The nonpiezoelectric plate is made of a material such that thephase velocity of the surface acoustic wave traveling on thenonpiezoelectric plate alone is higher than that traveling on thepiezoelectric substrates P_(T) and P_(R) alone. The interdigitaltransducers T_(i) and R_(i1) form N propagation lanes D_(i1) (i=1, 2, .. . , N) of the surface acoustic wave on the upper end surface of thenonpiezoelectric plate. The interdigital transducers T_(i) and R_(i2)form N propagation lanes D_(i2) (i=1, 2, . . . , N) of the surfaceacoustic wave on the upper end surface of the nonpiezoelectric plate.Two neighbors of the propagation lanes D_(i1) and D_(i2) are closed orpartially overlapping each other. The propagation lanes D_(i1) andD_(i2) of the surface acoustic wave transducing unit X and that of thesurface acoustic wave transducing unit Y are vertical to each other.Each propagation lane consists of minute propagation lanes Z_(j) (j=1,2, . . . , X) corresponding to the positions F_(j). If touching aposition F_(x) on a minute propagation lane Z_(x) out of the propagationlanes D_(i1) and D_(i2), an electric signal E with a phase θ isdelivered from one of the interdigital transducers R_(i1) and R_(i2),the position F_(x) corresponding to an electric signal E_(x) with aphase θ_(x), the total electric signal ΣE_(j) minus the electric signalE_(x) being equal to the electric signal E, the total phase Σθ_(j) minusthe phase θ_(x) being equal to the phase θ. The controlling systemsenses a touch with a finger or others on the position F_(x) by anappearance of the electric signal E at the one of the interdigitaltransducers R_(i1) and R_(i2), and finds the position F_(x) by detectingthe one, delivering the electric signal E, of the interdigitaltransducers R_(i1) and R_(i2), and by evaluating a difference betweenthe phases θ and θ_(base).

According to another aspect of the present invention there are providedN switches W_(i) (i=1, 2, . . . , N) corresponding to the interdigitaltransducers T_(i), an output terminal of each switch W_(i) beingconnected with an input terminal of each interdigital transducer T_(i).Output terminals of the interdigital transducers R_(i1) are connectedwith each other at an output point Q₁. Output terminals of theinterdigital transducers R_(i2) are connected with each other at anoutput point Q₂. The controlling system turns on and off the switchesW_(i) with a fixed period in turn, senses a touch on the position F_(x)by an appearance of the electric signal E at one of the output points Q₁and Q₂, and finds the position F_(x) by detecting the one, deliveringthe electric signal E, of the output points Q₁ and Q₂, by choosing aclosed one out of the switches W_(i) when the electric signal E appears,and by evaluating the difference between the phases θ and θ_(base).

According to another aspect of the present invention there is providedan amplifier A_(x), an input terminal of the interdigital transducerR_(o) of the surface acoustic wave transducing unit X being connectedwith each input terminal of the interdigital transducer T_(o) of thesurface acoustic wave transducing units X and Y via the amplifier A_(x).The interdigital transducers T_(o) and R_(o) in the surface acousticwave transducing unit X, a propagation lane of a surface acoustic wavebetween the interdigital transducers T_(o) and R_(o) in the surfaceacoustic wave transducing unit X, and the amplifier A_(x) form anoscillator.

According to another aspect of the present invention there is provided asurface acoustic wave position-sensing device comprising two surfaceacoustic wave transducing units X and Y, the nonpiezoelectric plate, andthe controlling system connected with the surface acoustic wavetransducing units X and Y. Each surface acoustic wave transducing unitconsists of the piezoelectric substrates P_(T) and P_(R), theinterdigital transducers T_(o), R_(o), R_(i1) and R_(i2), N inputinterdigital transducers M_(i) (i=1, 2, . . . , N) in place of theinterdigital transducers T_(i) formed on the upper end surface of thepiezoelectric substrate P_(T), N earth electrodes G_(i) (i=1, 2, . . . ,N) formed on the lower end surface of the piezoelectric substrate P_(T)and corresponding with the interdigital transducers M_(i), respectively,and a phase shifter S including at least a coil L₁. Each interdigitaltransducer M_(i) having the same interdigital periodicity as theinterdigital periodicity P, consists of two electrodes M_(i-1) andM_(i-2) and has two kinds of distances between one electrode finger ofthe electrode M_(i-1) and two neighboring electrode fingers of theelectrode M_(i-2). Each of the interdigital transducers R_(i1) andR_(i2) is placed such that the finger direction thereof is slanting tothat of the interdigital transducer M_(i) by an angle α, respectively.

When electric signals V₁ and V₂, with a frequency approximatelycorresponding to the interdigital periodicity P, are applied between theelectrode M_(i-1) and the earth electrode G_(i), and between theelectrode M_(i-2) and the earth electrode G_(i) via the phase shifter S,respectively, an unidirectional surface acoustic wave of the first modeand the higher order modes is excited in the piezoelectric substrateP_(T), on condition that x<1/2 in a shorter distance xP of the two kindsof distances between one electrode finger of the electrode M_(i-1) andtwo neighboring electrode fingers of the electrode M_(i-2), and x+y=±1/2in a phase difference 2πy between the electric signals V₁ and V₂. Theunidirectional surface acoustic wave is transmitted to the piezoelectricsubstrate P_(R) through the upper end surface of the nonpiezoelectricplate. The unidirectional surface acoustic wave excited by eachinterdigital transducer M_(i) and each earth electrode G_(i) istransduced to electric signals E_(j) with phases θ_(j), respectively,the phases θ_(j) corresponding to the positions F_(j). The interdigitaltransducers M_(i) and R_(i1) form N propagation lanes D_(i1) of thesurface acoustic wave on the upper end surface of the nonpiezoelectricplate. The interdigital transducers M_(i) and R_(i2) form N propagationlanes D_(i2) of the surface acoustic wave on the upper end surface ofthe nonpiezoelectric plate. Each propagation lanes D_(i1) and D_(i2)consists of minute propagation lanes Z_(j) corresponding to thepositions F_(j). If touching a position F_(x) on a minute propagationlane Z_(x), an electric signal E with a phase θ is delivered from one ofthe interdigital transducers R_(i1) and R_(i2). The controlling systemsenses a touch with a finger or others on the position F_(x) by anappearance of the electric signal E at the one of the interdigitaltransducers R_(i1) and R_(i2), and finds the position F_(x) by detectingthe one, delivering the electric signal E, of the interdigitaltransducers R_(i1) and R_(i2), and by evaluating a difference betweenthe phases θ and θ_(base).

According to another aspect of the present invention there are providedpiezoelectric substrates P_(T) and P_(R) made of a piezoelectricceramic, the polarization axis thereof being parallel to the thicknessdirection thereof.

According to other aspect of the present invention there are providedpiezoelectric substrates P_(T) and P_(R) made of a piezoelectric polymersuch as PVDF and so on.

According to a further aspect of the present invention there is provideda supporting board cemented to the lower end surface of thenonpiezoelectric plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be clarified fromthe following description with reference to the attached drawings.

FIG. 1 shows a sectional view of a surface acoustic waveposition-sensing device according to a first embodiment of the presentinvention.

FIG. 2 shows a plan view of the surface acoustic wave position-sensingdevice in FIG. 1.

FIG. 3 shows a fragmentary plan view, on an enlarged scale, of thesurface acoustic wave position-sensing device in FIG. 1.

FIG. 4 shows a plan view of interdigital transducer (R_(X11)).

FIG. 5 shows a diagram of a driving circuit of the surface acoustic waveposition-sensing device in FIG. 1.

FIG. 6 shows a relationship between the k² value calculated from thedifference between the phase velocity under electrically openedcondition and that under electrically shorted condition of piezoelectricsubstrate (P_(TX)), and the fd value.

FIG. 7 shows a relationship between the phase velocity of the surfaceacoustic wave for each mode in piezoelectric substrate (P_(TX)), and thefd value.

FIG. 8 shows a relationship between the k² value and the fd value.

FIG. 9 shows a relationship between the phase velocity of the surfaceacoustic wave with each mode in piezoelectric substrate (P_(TX)), andthe fd value.

FIG. 10 shows a relationship between a touch-position F_(x) and a phasedifference (θ_(base) -θ) detected by phase comparator (4).

FIG. 11 shows a fragmentary sectional view of a surface acoustic waveposition-sensing device according to a second embodiment of the presentinvention.

FIG. 12 shows a fragmentary plan view, on an enlarged scale, of thesurface acoustic wave position-sensing device in FIG. 11.

FIG. 13 shows a plan view of interdigital transducer (M_(X1)).

FIG. 14 shows a diagram of a driving circuit of the surface acousticwave position-sensing device in FIG. 11.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS

FIG. 1 shows a sectional view of a surface acoustic waveposition-sensing device according to a first embodiment of the presentinvention. The surface acoustic wave position-sensing device comprisesnonpiezoelectric plate (1) having an upper- and a lower end surfacesrunning perpendicular to the thickness direction thereof, supportingboard (2), controlling system (3), switches (W₁ and W₂), amplifier(A_(x)) and surface acoustic wave transducing units (X and Y). Surfaceacoustic wave transducing unit (X) comprises piezoelectric substrate(P_(TX)) having an upper- and a lower end surfaces running perpendicularto the direction of the thickness d thereof, piezoelectric substrate(P_(RX)) having an upper- and a lower end surfaces running perpendicularto the direction of the thickness d thereof, input interdigitaltransducers (T_(X0), T_(X1) and T_(X2)), and output interdigitaltransducers (R_(X0), R_(X11), R_(X12), R_(X13), R_(X14), R_(X21),R_(X22), R_(X23) and R_(X24)). Surface acoustic wave transducing unit(Y) comprises piezoelectric substrate (P_(TY)) having an upper- and alower end surfaces running perpendicular to the direction of thethickness d thereof, piezoelectric substrate (P_(RY)) having an upper-and a lower end surfaces running perpendicular to the direction of thethickness d thereof, input interdigital transducers (T_(Y0), T_(Y1) andT_(Y2)) and output interdigital transducers (R_(Y0), R_(Y11), R_(Y12),R_(Y13), RY₁₄, R_(Y21), R_(Y22), R_(Y23) and R_(Y24)). FIG. 1 shows onlynonpiezoelectric plate (1), supporting board (2), piezoelectricsubstrates (P_(TX) and P_(RX)), and interdigital transducers (T_(X1) andR_(X11)). Each piezoelectric substrate, of which material ispiezoelectric ceramic and having a dimension of 150 μm in thickness, iscemented on the upper end surface of nonpiezoelectric plate (1), ofwhich material is glass and having a dimension of 1.5 mm in thickness,through an epoxy resin with thickness of about 20 μm. The lower endsurface of nonpiezoelectric plate (1) is cemented on supporting board(2).

FIG. 2 shows a plan view of the surface acoustic wave position-sensingdevice in FIG. 1. FIG. 2 shows only nonpiezoelectric plate (1), thepiezoelectric substrates, and the interdigital transducers made fromaluminium thin film. Interdigital transducers (T_(X0), T_(X1) andT_(X2)) are mounted on the upper end surface of piezoelectric substrate(P_(TX)). Interdigital transducers (R_(X0), R_(X11), R_(X12), R_(X13),R_(X14), R_(X21), R_(X22), R_(X23) and R_(X24)) are mounted on the upperend surface of piezoelectric substrate (P_(RX)). Interdigitaltransducers (T_(Y0), T_(Y1) and T_(Y2)) are mounted on the upper endsurface of piezoelectric substrate (P_(TY)). Interdigital transducers(R_(Y0), R_(Y11), R_(Y12), R_(Y13), R_(Y14), R_(Y21), R_(Y22), R_(Y23)and R_(Y24)) are mounted on the upper end surface of piezoelectricsubstrate (P_(RY)). Two neighboring piezoelectric substrates, forexample, piezoelectric substrates (P_(TX) and P_(TY)), can be linked toeach other. Thus, it is possible to use only one body formed bypiezoelectric substrates (P_(TX), P_(TY), P_(RX) and P_(RY)). Inaddition, the interdigital transducers can be mounted on the lower endsurface of piezoelectric substrates (P_(TX), P_(RX), P_(TY) and P_(RY)),that is between nonpiezoelectric plate (1) and piezoelectric substrates(P_(TX), P_(RX), P_(TY) and P_(RY)). Interdigital transducers (T_(X0),R_(X0), T_(Y0) and R_(Y0)) have the same common-type constructions withan overlap length shorter than that of interdigital transducers (T_(X1),T_(X2), T_(Y1) and T_(Y2)) having the same common-type constructions.Interdigital transducers (R_(X11), R_(X12), R_(X13), R_(X14), R_(X21),R_(X22), R_(X23), R_(X24), R_(Y11), R_(Y12), R_(Y13), R_(Y14), R_(Y21),R_(Y22), R_(Y23) and R_(Y24)) have the same constructions. The fingerdirection of interdigital transducers (R_(X11), R_(X12), R_(X13),R_(X14), R_(X21), R_(X22), R_(X23) and R_(X24)) is not parallel to thatof interdigital transducers (T_(X1) and T_(X2)). The finger direction ofinterdigital transducers (R_(Y11), R_(Y12), R_(Y13), R_(Y14), R_(Y21),R_(Y22), R_(Y23) and R_(Y24)) is not parallel to that of interdigitaltransducers (T_(Y1) and T_(Y2)).

FIG. 3 shows a fragmentary plan view, on an enlarged scale, of thesurface acoustic wave position-sensing device in FIG. 1. FIG. 3 showsonly nonpiezoelectric plate (1), the piezoelectric substrates, and theinterdigital transducers consisting of ten finger pairs, respectively.Each of interdigital transducers (T_(X0), R_(X0), T_(Y0) and R_(Y0)) hasan interdigital periodicity P of 400 μm and an overlap length of 1 mm.Each of interdigital transducers (T_(X1), T_(X2), T_(Y1) and T_(Y2)) hasan interdigital periodicity P of 400 μm and an overlap length L of 12mm. The sum of each overlap length L_(N), along the finger direction ofinterdigital transducer (T_(X1)), of interdigital transducers (R_(X11),R_(X12), R_(X13) and R_(X14)) is equal to the overlap length L. The sumof each overlap length L_(N), along the finger direction of interdigitaltransducer (T_(X2)), of interdigital transducers (R_(X21), R_(X22),R_(X23) and R_(X24)) is equal to the overlap length L. The sum of eachoverlap length L_(N), along the finger direction of interdigitaltransducer (T_(Y1)), of interdigital transducers (R_(Y11), R_(Y12),R_(Y13) and R_(Y14)) is equal to the overlap length L. The sum of eachoverlap length L_(N), along the finger direction of interdigitaltransducer (T_(Y2)), of interdigital transducers (R_(Y21), R_(Y22),R_(Y23) and R_(Y24)) is equal to the overlap length L. In the surfaceacoustic wave position-sensing device, it is possible to sense a touchwith a finger or others on one of positions F_(j) (j=1, 2, . . . , X),along the finger direction of interdigital transducer (T_(X1) orT_(X2)), within each overlap length L_(N) of interdigital transducers(R_(X11), R_(X12), R_(X13), R_(X14), R_(X21), R_(X22), R_(X23) andR_(X24)) on the upper end surface of non piezoelectric plate (1). In thesame way, it is possible to sense a touch with a finger or others on oneof positions F_(x) (j=1, 2, . . . , X), along the finger direction ofinterdigital transducer (T_(Y1) or T_(Y2)), within each overlap lengthL_(N) of interdigital transducers (R_(Y11), R_(Y12), R_(Y13), R_(Y14),R_(Y21), R_(Y22), R_(Y23) and R_(Y24)) on the upper end surface of nonpiezoelectric plate (1).

FIG. 4 shows a plan view of interdigital transducer (R_(x11)). Each ofinterdigital transducers (R_(X11), R_(X12), R_(X13), R_(X14), R_(X21),R_(X22), R_(X23) and R_(X24)) is located such that the finger directionthereof is slanting to that of interdigital transducer (T_(X1) orT_(X2)) by an angle α. In the same way, each of interdigital transducers(R_(Y11), R_(Y12), R_(Y13), R_(Y14), R_(Y21), R_(Y22), R_(Y23) andR_(Y24)) is located such that the finger direction thereof is slantingto that of interdigital transducer (T_(Y1) or T_(Y2)) by an angle α. Aninterdigital periodicity P_(N), along the vertical direction to thefinger direction of interdigital transducers (R_(X11), R_(X12), R_(X13),R_(X14), R_(X21), R_(X22), R_(X23) and R_(X24)) is equal to the productof the interdigital periodicity P and cos α. In the same way, aninterdigital periodicity P_(N), along the vertical direction to thefinger direction of interdigital transducers (R_(Y11), R_(Y12), R_(Y13),R_(Y14), R_(Y21), R_(Y22), R_(Y23) and R_(Y24)) is equal to the productof the interdigital periodicity P and cos α. Each overlap length L_(P),along the finger direction of interdigital transducers (R_(X11),R_(X12), R_(X13) and R_(X14)), of interdigital transducers (R_(X11),R_(X12), R_(X13) and R_(X14)) is equal to the product of the overlaplength L_(N) and sec α. In other words, the sum of each overlap lengthL_(P) of interdigital transducers (R_(X11), R_(X12), R_(X13) andR_(X14)) is equal to the product of the overlap length L and sec α. Inthe same way, the sum of each overlap length L_(P) of interdigitaltransducers (R_(X21), R_(X22), R_(X23) and R_(X24)) is equal to theproduct of the overlap length L and sec α. The sum of each overlaplength L_(P) of interdigital transducers (R_(Y11), R_(Y12), R_(Y13) andR_(Y14)) is equal to the product of the overlap length L and sec α. Thesum of each overlap length L_(P) of interdigital transducers (R_(Y21),R_(Y22), R_(Y23) and R_(Y24)) is equal to the product of the overlaplength L and sec α.

FIG. 5 shows a diagram of a driving circuit of the surface acoustic waveposition-sensing device in FIG. 1. Controlling system (3) compriseseight phase comparators (4), computer (5) and switch-change unit (6).Output terminal of switch (W₁) is connected with input terminals ofinterdigital transducers (T_(X1) and T_(Y1)). Output terminal of switch(W₂) is connected with input terminals of interdigital transducers(T_(X2) and T_(Y2)). A point Q_(X1) joining output terminals ofinterdigital transducers (R_(X11) and R_(X21)), a point Q_(X2) joiningoutput terminals of interdigital transducers (R_(X12) and R_(X22)), apoint Q_(X3) joining output terminals of interdigital transducers(R_(X13) and R_(X23)), and a point Q_(X4) joining output terminals ofinterdigital transducers (R_(X14) and R_(X24)) are connected with phasecomparators (4) via amplifiers (AMP), respectively. In the same way, apoint Q_(Y1) joining output terminals of interdigital transducers(R_(Y11) and R_(Y21)), a point Q_(Y2) joining output terminals ofinterdigital transducers (R_(Y12) and R_(Y22)), a point Q_(Y3) joiningoutput terminals of interdigital transducers (R_(Y13) and R_(Y23)), anda point Q_(Y4) joining output terminals of interdigital transducers(R_(Y14) and R_(Y24)) are connected with phase comparators (4) viaamplifiers (AMP), respectively.

In the driving circuit in FIG. 5, when an electric signal having afrequency approximately corresponding to the interdigital periodicity Pis applied to interdigital transducers (T_(X0), T_(X1) and T_(X2)),respectively, the surface acoustic wave, of the first mode and thehigher order modes, having the wavelength approximately equal to theinterdigital periodicity P is excited in piezoelectric substrate(P_(TX)) effectively. In this time, if the phase velocity of the surfaceacoustic wave of the first mode and the higher order modes isapproximately equal to the phase velocity of the Rayleigh wave travelingon nonpiezoelectric plate (1) alone, the transducing efficiency from theelectric signal to the surface acoustic wave increases, and in addition,the reflection caused by the miss-matching on the acoustic impedance atthe boundary surface between piezoelectric substrate (P_(TX)) andnonpiezoelectric plate (1) never causes. In addition, as piezoelectricsubstrate (P_(TX)) is made from a piezoelectric ceramic having thepolarization axis parallel to the thickness direction thereof, thesurface acoustic wave of the first mode and the higher order modes isexcited in piezoelectric substrate (P_(TX)) effectively, and thetransducing efficiency from the electric signal to the surface acousticwave increases. If using a piezoelectric polymer such as PVDF and so on,as piezoelectric substrate (P_(TX)), the surface acoustic wave of thefirst mode and the higher order modes is excited in piezoelectricsubstrate (P_(TX)) effectively, and the transducing efficiency from theelectric signal to the surface acoustic wave increases.

The surface acoustic wave excited in piezoelectric substrate (P_(TX)) istransmitted to the upper end surface of nonpiezoelectric plate (1). Asthe the thickness d of piezoelectric substrate (P_(TX)) is smaller thanthe interdigital periodicity P, and the thickness of nonpiezoelectricplate (1) is larger than three times the interdigital periodicity P, itis possible to increase the transmitting efficiency of the surfaceacoustic wave from piezoelectric substrate (P_(TX)) to the upper endsurface of nonpiezoelectric plate (1), without a leakage of the surfaceacoustic wave on the inside of nonpiezoelectric plate (1). In addition,if using a material, as nonpiezoelectric plate (1), such that the phasevelocity of the surface acoustic wave traveling on nonpiezoelectricplate (1) alone is higher than that traveling on piezoelectric substrate(P_(TX)) alone, it is possible to increase the transmitting efficiencyof the surface acoustic wave from piezoelectric substrate (P_(TX)) tothe upper end surface of nonpiezoelectric plate (1) without a leakage ofthe surface acoustic wave on the inside of nonpiezoelectric plate (1).Thus, it is possible to operate the surface acoustic waveposition-sensing device under low power consumption and low voltage, andmoreover, it is possible to support the lower end surface ofnonpiezoelectric plate (1) by supporting board (2) directly

The surface acoustic wave excited by interdigital transducer (T_(X0)) istransmitted to piezoelectric substrate (P_(RX)) through the upper endsurface of nonpiezoelectric plate (1), and is transduced to an electricsignal with a phase θ_(base) by interdigital transducer (R_(X0)), theelectric signal being delivered from interdigital transducer (R_(X0))and amplified by amplifier (A_(x)). An electric signal 1 is applied tointerdigital transducers (T_(X0) and T_(Y0)). Thus, interdigitaltransducers (T_(X0) and R_(X0)), a propagation lane, as a delay element,of the surface acoustic wave between interdigital transducers (T_(X0)and R_(X0)), and amplifier (A_(x)) form an oscillator, causing not onlya low voltage operation and low power consumption, but also asmall-sized circuit with a simple structure. An electric signal 2 isapplied to four phase comparators (4).

The surface acoustic wave excited by interdigital transducer (T_(X1)) istransmitted to piezoelectric substrate (P_(RX)) through the upper endsurface of nonpiezoelectric plate (1), and is transduced to electricsignals E_(j) (j=1, 2, . . . , X) with phases θ_(j) (j=1, 2, . . . , X)by each of interdigital transducers (R_(X11), R_(X12), R_(X13) andR_(X14)), the phases θ_(j) corresponding to the positions F_(j),respectively. The surface acoustic wave excited by interdigitaltransducer (T_(X2)) is transmitted to piezoelectric substrate (P_(RX))through the upper end surface of nonpiezoelectric plate (1), and istransduced to electric signals E_(j) (j=1, 2, . . . , X) with phasesθ_(j) (j=1, 2, . . . , X) by each of interdigital transducers (R_(X21),R_(X22), R_(X23) and R_(X24)), the phases θ_(j) corresponding to thepositions F_(j), respectively. Each electric signal E_(j) has afrequency approximately corresponding to the interdigital periodicity P.The total phase Σθ_(j) made by phases θ_(j) is zero. The total electricsignal ΣE_(j) made by electric signals E_(j) is also zero and is notable to be detected at each of interdigital transducers (R_(X11),R_(X12), R_(X13), R_(X14), R_(X21), R_(X22), R_(X23) and R_(X24)).

As mentioned above, the surface acoustic wave excited in piezoelectricsubstrate (P_(TX)) is transmitted to piezoelectric substrate (P_(RX))through the upper end surface of nonpiezoelectric plate (1), and istransduced to the electric signal. In this time, if the phase velocityof the surface acoustic wave is approximately equal to the phasevelocity of the Rayleigh wave traveling on nonpiezoelectric plate (1)alone, the transducing efficiency from the surface acoustic wave to theelectric signal increases, and in addition, the reflection caused by themiss-matching on the acoustic impedance at the boundary surface betweenpiezoelectric substrate (P_(RX)) and nonpiezoelectric plate (1) nevercauses. In addition, as piezoelectric substrate (P_(RX)) is made from apiezoelectric ceramic having the polarization axis parallel to thethickness direction thereof, the transducing efficiency from the surfaceacoustic wave to the electric signal increases. If using a piezoelectricpolymer such as PVDF and so on, as piezoelectric substrate (P_(RX)), thetransducing efficiency from the surface acoustic wave to the electricsignal increases. As the the thickness d of piezoelectric substrate(P_(RX)) is smaller than the interdigital periodicity P, and thethickness of nonpiezoelectric plate (1) is larger than three times theinterdigital periodicity P, it is possible to increase the transmittingefficiency of the surface acoustic wave from the upper end surface ofnonpiezoelectric plate (1) to piezoelectric substrate (P_(RX)) without aleakage of the surface acoustic wave on the inside of nonpiezoelectricplate (1). If using a material, as nonpiezoelectric plate (1), such thatthe phase velocity of the surface acoustic wave traveling onnonpiezoelectric plate (1) alone is higher than that traveling onpiezoelectric substrate (P_(RX)) alone, it is possible to increase thetransmitting efficiency of the surface acoustic wave from the upper endsurface of nonpiezoelectric plate (1) to piezoelectric substrate(P_(RX)) without a leakage of the surface acoustic wave on the inside ofnonpiezoelectric plate (1). Thus, it is possible to operate the surfaceacoustic wave position-sensing device under low power consumption andlow voltage, and in addition, it is possible to support the lower endsurface of nonpiezoelectric plate (1) by supporting board (2) directly.

In the same way as the case of surface acoustic wave transducing unit(X) mentioned above, when an electric signal having a frequencyapproximately corresponding to the interdigital periodicity P is appliedto interdigital transducers (T_(Y0), T_(Y1) and T_(Y2)), respectively,the surface acoustic wave, of the first mode and the higher order modes,having the wavelength approximately equal to the interdigitalperiodicity P is excited in piezoelectric substrate (P_(TY))effectively. The surface acoustic wave excited by interdigitaltransducer (T_(Y0)) is transmitted to piezoelectric substrate (P_(RY))through the upper end surface of nonpiezoelectric plate (1), and istransduced to an electric signal with a phase θ_(base) by interdigitaltransducer (R_(Y0)), the electric signal being delivered frominterdigital transducer (R_(Y0)) and amplified by amplifier (A_(x)). Anelectric signal 3 is applied to switch-change unit (6), and an electricsignal 4 is applied to four phase comparators (4). Switch-change unit(6) under a control of computer (5) turns on and off switches (W₁ andW₂) alternately, and supplies a group of interdigital transducers(T_(X1) and T_(Y1)), and a group of interdigital transducers (T_(X2) andT_(Y2)) with the electric signal 3 alternately. The surface acousticwave excited by interdigital transducer (T_(Y1)) is transmitted topiezoelectric substrate (P_(RY)) through the upper end surface ofnonpiezoelectric plate (1), and is transduced to electric signals E_(j)(j=1, 2, . . . , X) with phases θ_(j) (j=1, 2, . . . , X) by each ofinterdigital transducers (R_(Y11), R_(Y12), R_(Y13) and R_(Y14)), thephases θ_(j) corresponding to the positions F_(j), respectively. Thesurface acoustic wave excited by interdigital transducer (T_(Y2)) istransmitted to piezoelectric substrate (P_(RY)) through the upper endsurface of nonpiezoelectric plate (1), and is transduced to electricsignals E_(j) (j=1, 2, . . . , X) with phases θ_(j) (j=1, 2, . . . , X)by each of interdigital transducers (R_(Y21), R_(Y22), R_(Y23) andR_(Y24)), the phases θ_(j) corresponding to the positions F_(j),respectively. Each electric signal E_(j) has a frequency approximatelycorresponding to the interdigital periodicity P. The total phase Σθ_(j)made by phases θ_(j) is zero. The total electric signal ΣE_(j) made byelectric signals E_(j) is also zero and is not able to be detected ateach of interdigital transducers (R_(Y11), R_(Y12), R_(Y13), R_(Y14),R_(Y21), R_(Y22), R_(Y23) and R_(Y24)).

Interdigital transducer (T_(X1)) and interdigital transducers (R_(X11),R_(X12), R_(X13) and R_(X14)) form four propagation lanes (D_(X11),D_(X12), D_(X13) and D_(X14)) of the surface acoustic wave on the upperend surface of nonpiezoelectric plate (1), respectively, eachpropagation lane consisting of minute propagation lanes Z_(j) (j=1, 2, .. . , X) corresponding to the positions F_(j). Interdigital transducer(T_(X2)) and interdigital transducers (R_(X21), R_(X22), R_(X23) andR_(X24)) form four propagation lanes (D_(X21), D_(X22), D_(X23) andD_(X24)) of the surface acoustic wave on the upper end surface ofnonpiezoelectric plate (1), respectively, each propagation laneconsisting of minute propagation lanes Z_(j) (j=1, 2, . . . , X)corresponding to the positions F_(j). In the same way, interdigitaltransducer (T_(Y1)) and interdigital transducers (R_(Y11), R_(Y12),R_(Y13) and R_(Y14)) form four propagation lanes (D_(Y11), D_(Y12),D_(Y13) and D_(Y14)) of the surface acoustic wave on the upper endsurface of nonpiezoelectric plate (1), respectively, each propagationlane consisting of minute propagation lanes Z_(j) (j=1, 2, . . . , X)corresponding to the positions F_(j). Interdigital transducer (T_(Y2))and interdigital transducers (R_(Y21), R_(Y22), R_(Y23) and R_(Y24))form four propagation lanes (D_(Y21), D_(Y22), D_(Y23) and D_(Y24)) ofthe surface acoustic wave on the upper end surface of nonpiezoelectricplate (1), respectively, each propagation lane consisting of minutepropagation lanes Z_(j) (j=1, 2, . . . , X) corresponding to thepositions F_(j).

When touching a position F_(x), out of the positions F_(j), on a minutepropagation lane Z_(x) out of the minute propagation lanes Z_(j) of oneof the propagation lanes (D_(X11), D_(X12), D_(X13), D_(X14), D_(X21),D_(X22), D_(X23) and D_(X24)), an electric signal E with a phase θ isdelivered from one of interdigital transducers (R_(X11), R_(X12),R_(X13), R_(X14), R_(X21), R_(X22), R_(X23) and R_(X24)). In this time,only the surface acoustic wave on the minute propagation lane Z_(x) isdisappeared and is not transduced to an electric signal E_(x) with aphase θ_(x). As a result, the electric signal E being equal to the totalelectric signal ΣE_(j) minus the electric signal E_(x) is delivered fromone of interdigital transducers (R_(X11), R_(X12), R_(X13), R_(X14),R_(X21), R_(X22), R_(X23) and R_(X24)), the phase θ being equal to thetotal phase Σθ_(j) minus the phase θ_(x), that is (θ=Σθ_(j) -θ_(x)=-θ_(x)). Phase comparator (4) detects a difference between the phase θand the phase θ_(base), only when the phase comparator (4) is appliedwith the electric signal E. Computer (5) finds the position F_(x) fromthe phase difference (θ_(base) -θ). In the same way, when touching aposition F_(x) on a minute propagation lane Z_(x) out of one of thepropagation lanes (D_(Y11), D_(Y12), D_(Y13), D_(Y14), D_(Y21), D_(Y22),D_(Y23) and D_(Y24)), an electric signal E with a phase θ is deliveredfrom one of interdigital transducers (R_(Y11), R_(Y12), R_(Y13),R_(Y14), R_(Y21), R_(Y22), R_(Y23) and R_(Y24)). In this time, only thesurface acoustic wave on the minute propagation lane Z_(x) isdisappeared and is not transduced to an electric signal E_(x) with aphase θ_(x), the electric signal E being equal to the total electricsignal ΣE_(j) minus the electric signal E_(x), the phase θ being equalto the total phase Σθ_(j) minus the phase θ_(x). Phase comparator (4)detects a difference between the phase θ and the phase θ_(base), onlywhen the phase comparator (4) is applied with the electric signal E.Computer (5) finds the position F_(x) from the phase difference(θ_(base) -θ).

As mentioned previously, switch-change unit (6) under a control ofcomputer (5) turns on and off switches (W₁ and W₂) alternately. At thesame time, computer (5) detects switch (W₁ or W₂) closed when theelectric signal E appears at one of the points Q_(X1), Q_(X2), Q_(X3)and Q_(X4). Thus, for example, if switch (W₂) is closed when theelectric signal E appears at the point Q_(X3), it is clear that theelectric signal E is delivered from interdigital transducer (R_(X23)).Therefore, it is clear that the touch-position F_(x) is on the minutepropagation lane Z_(x) out of the propagation lane (D_(X23)). In thesame way, computer (5) detects switch (W₁ or W₂) closed when theelectric signal E appears at the point Q_(Y1), Q_(Y2), Q_(Y3) andQ_(Y4). For example, if switch (W₁) is closed when the electric signal Eappears at the point Q_(Y1), it is clear that the touch-position F_(x)is on the minute propagation lane Z_(x) out of the propagation lane(D_(Y11)). Since eight propagation lanes (D_(X11), D_(X12), D_(X13),D_(X14), D_(X21), D_(X22), D_(X23) and D_(X24)) and eight propagationlanes (D_(Y11), D_(Y12), D_(Y13), D_(Y14), D_(Y21), D_(Y22), D_(Y23) andD_(Y24)) cross each other, it is clear that the touch-position F_(x)exists on a crossing point made by the minute propagation lane Z_(x) outof the propagation lane (D_(X23)) and the minute propagation lane Z_(x)out of the propagation lane (D_(Y11)). In addition, eight propagationlanes (D_(X11), D_(X12), D_(X13), D_(X14), D_(X21), D_(X22), D_(X23) andD_(X24)) are closed each other, and eight propagation lanes (D_(Y11),D_(Y12), D_(Y13), D_(Y14), D_(Y21), D_(Y22), D_(Y23) and D_(Y24)) arealso closed each other. Accordingly, there is no null touch-point on theupper end surface of nonpiezoelectric plate (1). In order to make nonull touch-point, it is also effective to arrange eight propagationlanes (D_(X11), D_(X12), D_(X13), D_(X14), D_(X21), D_(X22), D_(X23) andD_(X24)) as they are partially overlapping each other, and arrange eightpropagation lanes (D_(Y11), D_(Y12), D_(Y13), D_(Y14), D_(Y21), D_(Y22),D_(Y23) and D_(Y24)) as they are partially overlapping each other.

FIG. 6 shows a relationship between the electromechanical couplingconstant k² calculated from the difference between the phase velocityunder electrically opened condition and that under electrically shortedcondition of piezoelectric substrate (P_(TX)), and the product fd of thefrequency f of the surface acoustic wave and the thickness d ofpiezoelectric substrate (P_(TX)). In FIG. 6, nonpiezoelectric plate (1)is made from a glass having a shear wave velocity of 3091 m/s and alongitudinal wave velocity of 5592 m/s traveling on the glass alone. Thevelocities of 3091 m/s and 5592 m/s are about 1.3 times the velocitiesof a shear- and a longitudinal waves, 2450 m/s and 4390 m/s,respectively, in piezoelectric substrate (P_(TX)) alone. An electricenergy applied to the input interdigital transducer is most easilytransduced to the first mode surface acoustic wave when the fd value isapproximately 1.3 MHz.mm, then the k² value is approximately 4.7% beingthe maximum value. It is clear that the k² value of 4.7% is worthy incomparison that a crystallized LiNbO₃ used as a popular piezoelectricbody for exciting a surface acoustic wave generally has the k² value ofapproximately 5%.

FIG. 7 shows a relationship between the phase velocity of the surfaceacoustic wave for each mode in piezoelectric substrate (P_(TX)), and thefd value. In FIG. 7, nonpiezoelectric plate (1) is made from the sameglass as FIG. 6. The fd value at each mark ∘ has the maximum k² valuewhere an electric energy applied to the input interdigital transducer ismost easily transduced to the surface acoustic wave, the maximum k²value being obtained from FIG. 6. The phase velocity of the surfaceacoustic wave of the first mode and the higher order modes at the mark ∘is approximately 2980 m/s, which is approximately equal to the phasevelocity of the Rayleigh wave traveling on nonpiezoelectric plate (1)alone, the phase velocity of the Rayleigh wave being 2850 m/s.

FIG. 8 shows a relationship between the k² value and the fd value. InFIG. 8, nonpiezoelectric plate (1) is made from a glass having a shearwave velocity of 4203 m/s and a longitudinal wave velocity of 7604 m/straveling on the glass alone. The velocities of 4203 m/s and 7604 m/sare about 1.7 times the velocities of a shear- and a longitudinal waves,2450 m/s and 4390 m/s, respectively, in piezoelectric substrate (P_(TX))alone. An electric energy applied to the input interdigital transduceris most easily transduced to the first mode surface acoustic wave whenthe fd value is approximately 0.7 MHz.mm, then the k² value isapproximately 14.0% being the maximum value.

FIG. 9 shows a relationship between the phase velocity of the surfaceacoustic wave with each mode in piezoelectric substrate (P_(TX)), andthe fd value. In FIG. 9, nonpiezoelectric plate (1) is made from thesame glass as FIG. 8. The fd value at each mark ∘ has the maximum k²value where an electric energy applied to the input interdigitaltransducer is most easily transduced to the surface acoustic wave, themaximum k² value being obtained from FIG. 8. The phase velocity of thesurface acoustic wave of the first mode and the higher order modes atthe mark ∘ is approximately 3800 m/s, which is approximately equal tothe phase velocity of the Rayleigh wave traveling on nonpiezoelectricplate (1) alone, the phase velocity of the Rayleigh wave being 3860 m/s.

It is clear from FIGS. 6˜9 that an electric energy applied to the inputinterdigital transducer is most easily transduced to the surfaceacoustic wave of the first mode and the higher order modes having thephase velocity approximately equal to the phase velocity of the Rayleighwave traveling on nonpiezoelectric plate (1) alone. In the same way, thesurface acoustic wave, of the first mode and the higher order modes,having the phase velocity approximately equal to the phase velocity ofthe Rayleigh wave traveling on nonpiezoelectric plate (1) alone, is mosteasily transduced to an electric signal at the output interdigitaltransducer.

FIG. 10 shows a relationship between a touch-position F_(x) and a phasedifference (θ_(base) -θ) detected by phase comparator (4). The distancebetween the touch-position F_(x) and a touch-position F_(x+1) is 0.5 mm.There exists a linear relationship between the touch-position F_(x) andthe phase difference (θ_(base) -θ).

FIG. 11 shows a fragmentary sectional view of a surface acoustic waveposition-sensing device according to a second embodiment of the presentinvention. The surface acoustic wave position-sensing device comprisesnonpiezoelectric plate (1), supporting board (2), controlling system(3), a pair of switches (W₁₁ and W₁₂), a pair of switches (W₂₁ and W₂₂),amplifier (A_(x)), earth electrodes (G_(X1), G_(X2), G_(Y1) and G_(Y2)),phase shifter (S) and surface acoustic wave transducing units (X and Y).Surface acoustic wave transducing unit (X) in FIG. 11 has the sameconstruction as that in FIG. 1, except for using of interdigitaltransducers (M_(X1) and M_(X2)) in place of interdigital transducers(T_(X1) and T_(X2)). Surface acoustic wave transducing unit (Y) in FIG.11 has the same construction as that in FIG. 1, except for using ofinterdigital transducers (M_(Y1) and M_(Y2)) in place of interdigitaltransducers (T_(Y1) and T_(Y2)). FIG. 11 shows only nonpiezoelectricplate (1), supporting board (2), piezoelectric substrate (P_(TX)),interdigital transducer (M_(X1)), earth electrode (G_(X1)) and phaseshifter (S) including coil L₁. Earth electrodes (G_(X1), G_(X2), G_(Y1)and G_(Y2)), made from aluminium thin film, have the same constructions.Earth electrodes (G_(X1) and G_(X2)), corresponding with interdigitaltransducers (M_(X1) and M_(X2)), respectively, are formed on the lowerend surface of piezoelectric substrate (P_(TX)). Earth electrodes(G_(Y1) and G_(Y2)), corresponding with interdigital transducers (M_(Y1)and M_(Y2)), respectively, are formed on the lower end surface ofpiezoelectric substrate (P_(TY)).

FIG. 12 shows a fragmentary plan view, on an enlarged scale, of thesurface acoustic wave position-sensing device in FIG. 11. FIG. 12 showsonly nonpiezoelectric plate (1), the piezoelectric substrates, and theinterdigital transducers. Each of interdigital transducers (M_(X1),M_(X2), M_(Y1) and M_(Y2)) consists of ten finger pairs, and has aninterdigital periodicity P of 400 μm and an overlap length L of 12 mm.The sum of each overlap length L_(N), along the finger direction ofinterdigital transducer (M_(X1)), of interdigital transducers (R_(X11),R_(X12), R_(X13) and R_(X14)) is equal to the overlap length L. The sumof each overlap length L_(N), along the finger direction of interdigitaltransducer (M_(X2)), of interdigital transducers (R_(X21), R_(X22),R_(X23) and R_(X24)) is equal to the overlap length L. The sum of eachoverlap length L_(N), along the finger direction of interdigitaltransducer (M_(Y1)), of interdigital transducers (R_(Y11), R_(Y12),R_(Y13) and R_(Y14)) is equal to the overlap length L. The sum of eachoverlap length L_(N), along the finger direction of interdigitaltransducer (M_(Y2)), of interdigital transducers (R_(Y21), R_(Y22),R_(Y23) and R_(Y24)) is equal to the overlap length L. In the surfaceacoustic wave position-sensing device, it is possible to sense a touchon one of positions F_(j) (j=1, 2, . . . , X), along the fingerdirection of interdigital transducer (M_(X1) or M_(X2)), within eachoverlap length L_(N) of interdigital transducers (R_(X11), R_(X12),R_(X13), R_(X14), R_(X21), R_(X22), R_(X23) and R_(X24)) on the upperend surface of non piezoelectric plate (1). In the same way, it ispossible to sense a touch on one of positions F_(j) (j=1, 2, . . . , X),along the finger direction of interdigital transducer (M_(Y1) orM_(Y2)), within each overlap length L_(N) of interdigital transducers(R_(Y11), R_(Y12), R_(Y13), R_(Y14), R_(Y21), R_(Y22), R_(Y23) andR_(Y24)) on the upper end surface of non piezoelectric plate (1).

Each of interdigital transducers (R_(X11), R_(X12), R_(X13), R_(X14),R_(X21), R_(X22), R_(X23) and R_(X24)) is, as shown in FIG. 4, locatedsuch that the finger direction thereof is slanting to that ofinterdigital transducer (M_(X1) or M_(X2)) by an angle α. In the sameway, each of interdigital transducers (R_(Y11), R_(Y12), R_(Y13),R_(Y14), R_(Y21), R_(Y22), R_(Y23) and R_(Y24)) is located such that thefinger direction thereof is slanting to that of interdigital transducer(M_(Y1) and M_(Y2)) by an angle α. An interdigital periodicity P_(N),along the vertical direction to the finger direction of interdigitaltransducers (R_(X11), R_(X12), R_(X13), R_(X14), R_(X21), R_(X22),R_(X23) and R_(X24)) is, as as shown in FIG. 4, equal to the product ofthe interdigital periodicity P and cos α. In the same way, aninterdigital periodicity P_(N), along the vertical direction to thefinger direction of interdigital transducers (R_(Y11), R_(Y12), R_(Y13),R_(Y14), R_(Y21), R_(Y22), R_(Y23) and R_(Y24)) is equal to the productof the interdigital periodicity P and cos α. The sum of each overlaplength L_(P) of interdigital transducers (R_(X11), R_(X12), R_(X13) andR_(X14)) is equal to the product of the overlap length L and sec α. Inthe same way, the sum of each overlap length L_(P) of interdigitaltransducers (R_(X21), R_(X22), R_(X23) and R_(X24)) is equal to theproduct of the overlap length L and sec α. The sum of each overlaplength L_(P) of interdigital transducers (R_(Y11), R_(Y12), R_(Y13) andR_(Y14)) is equal to the product of the overlap length L and sec α. Thesum of each overlap length L_(P) of interdigital transducers (R_(Y21),R_(Y22), R_(Y23) and R_(Y24)) is equal to the product of the overlaplength L and sec α.

FIG. 13 shows a plan view of interdigital transducer (M_(X1)).Interdigital transducer (M_(X1)) consists of two electrodes (M_(X1-1)and M_(X1-2)), and has two kinds of distances between one electrodefinger of electrode (M_(X1-1)) and two neighboring electrode fingers ofelectrode (M_(X1-2)), a shorter distance xP of the two kinds ofdistances being 100 μm. Interdigital transducers (M_(X1), M_(X2), M_(Y1)and M_(Y2)), made from aluminium thin film, have the same constructionseach other.

FIG. 14 shows a diagram of a driving circuit of the surface acousticwave position-sensing device in FIG. 11. Controlling system (3)comprises eight phase comparators (4), computer (5) and switch-changeunit (6). Output terminal of switch (W₁₁) is connected with inputterminals of interdigital transducers (M_(X1-1) and M_(Y1-1)). Outputterminal of switch (W₁₂) is connected with input terminals ofinterdigital transducers (M_(X1-2) and M_(Y1-2)). Output terminal ofswitch (W₂₁) is connected with input terminals of interdigitaltransducers (M_(X2-1) and M_(Y2-1)). Output terminal of switch (W₂₂) isconnected with input terminals of interdigital transducers (M_(X2-2) andM_(Y2-2)). A point Q_(X1) joining output terminals of interdigitaltransducers (R_(X11) and R_(X21)), a point Q_(X2) joining outputterminals of interdigital transducers (R_(X12) and R_(X22)), a pointQ_(X3) joining output terminals of interdigital transducers (R_(X13) andR_(X22)), and a point Q_(X4) joining output terminals of interdigitaltransducers (R_(X14) and R_(X24)) are connected with phase comparators(4) via amplifiers (AMP), respectively. In the same way, a point Q_(Y1)joining output terminals of interdigital transducers (R_(Y11) andR_(Y22)), a point Q_(Y2) joining output terminals of interdigitaltransducers (R_(Y12) and R_(Y22)), a point Q_(Y3) joining outputterminals of interdigital transducers (R_(Y13) and R_(Y23)), and a pointQ_(Y4) joining output terminals of interdigital transducers (R_(Y14) andR_(Y24)) are connected with phase comparators (4) via amplifiers (AMP),respectively.

Interdigital transducers (T_(X0), R_(X0), T_(Y0) and R_(Y0)) in FIG. 14have the same function as that in FIG. 5. In addition, interdigitaltransducers (R_(X11), R_(X12), R_(X13), R_(X14), R_(X21), R_(X22),R_(X23), R_(X24), R_(Y11), R_(Y12), R_(Y13), R_(Y14), R_(Y21), R_(Y22),R_(Y23) and R_(Y24)) in FIG. 14 have the same function as that in FIG.5.

In the driving circuit in FIG. 14, electric signals V₁ and V₂, with afrequency approximately corresponding to the interdigital periodicity Pand having the phase difference 2πy, are applied between electrode(M_(X1-1)) and earth electrode (G_(X1)), and between electrode(M_(X1-2)) and earth electrode (G_(X1)), respectively. In this time, anunidirectional surface acoustic wave, of the first mode and the higherorder modes, having the wavelength approximately equal to theinterdigital periodicity P is excited in piezoelectric substrate(P_(TX)), on condition that x<1/2 in the shorter distance xP ofinterdigital transducer (M_(X1)), and x+y=±1/2 in the phase difference2πy. If x=1/4, y=1/4 or y=-3/4. Thus, the unidirectional surfaceacoustic wave is excited in piezoelectric substrate (P_(TX)), oncondition that xP=100 μm as shown in FIG. 13, and 2πy=π/2(90°) or2πy=-3π/2(-270°). The excitation of the unidirectional surface acousticwave generates no reflection of a surface acoustic wave at the sidesurface of piezoelectric substrate, so that seldom or never makes anoise. In addition, the excitation of the unidirectional surfaceacoustic wave reduces a waste of an electric energy applied tointerdigital transducer (M_(X1)), causing the surface acoustic waveposition-sensing device in FIG. 11 to be operated under low powerconsumption with low voltage.

As mentioned above, the unidirectional surface acoustic wave is excitedin piezoelectric substrate (P_(TX)) by interdigital transducer (M_(X1))and earth electrode (G_(X1)). In the same way, an unidirectional surfaceacoustic wave is excited in piezoelectric substrate (P_(TX)) byinterdigital transducer (M_(X2)) and earth electrode (G_(X2)). Anunidirectional surface acoustic wave is excited in piezoelectricsubstrate (P_(TY)) by interdigital transducer (M_(Y1)) and earthelectrode (G_(Y1)). An unidirectional surface acoustic wave is excitedin piezoelectric substrate (P_(TY)) by interdigital transducer (M_(Y2))and earth electrode (G_(Y2)). An electric signal 3 is applied toswitch-change unit (6) via phase shifter (S). Switch-change unit (6)under a control of computer (5) turns on and off the pair of switches(W₁₁ and W₁₂) and the pair of switches (W₂₁ and W₂₂) alternately, andsupplies a group of interdigital transducers (M_(X1) and M_(Y1)) and agroup of interdigital transducers (M_(X2) and M_(Y2)) with the electricsignal 3 alternately. In this time, switches (W₁₁ and W₁₂) are in thesame condition each other, and switches (W₂₁ and W₂₂) are in the samecondition each other.

The surface acoustic wave excited by interdigital transducer (M_(X1)) istransduced to electric signals E_(j) (j=1, 2, . . . , X) with phasesθ_(j) (j=1, 2, . . . , X) by each of interdigital transducers (R_(X11),R_(X12), R_(X13) and R_(X14)). The surface acoustic wave excited byinterdigital transducer (M_(X2)) is transduced to electric signals E_(j)(j=1, 2, . . . , X) with phases θ_(j) (j=1, 2, . . . , X) by each ofinterdigital transducers (R_(X21), R_(X22), R_(X23) and R_(X24)). Thesurface acoustic wave excited by interdigital transducer (M_(Y1)) istransduced to electric signals E_(j) (j=1, 2, . . . , X) with phasesθ_(j) (j=1, 2, . . . , X) by each of interdigital transducers (R_(Y11),R_(Y12), R_(Y13) and R_(Y14)). The surface acoustic wave excited byinterdigital transducer (M_(Y2)) is transduced to electric signals E_(j)(j=1, 2, . . . , X) with phases θ_(j) (j=1, 2, . . . , X) by each ofinterdigital transducers (R_(Y21), R_(Y22), R_(Y23) and R_(Y24)). Thephases θ_(j) correspond to the positions F_(j), respectively. Eachelectric signal E_(j) has a frequency approximately corresponding to theinterdigital periodicity P. The total phase Σθ_(j) made by the phasesθ_(j) is zero. The total electric signal ΣE_(j) made by the electricsignals E_(j) is also zero and is not able to be detected at each ofinterdigital transducers (R_(X11), R_(X12), R_(X13), R_(X14), R_(X21),R_(X22), R_(X23), R_(X24), R_(Y11), R_(Y12), R_(Y13), R_(Y14), R_(Y21),R_(Y22), R_(Y23) and R_(Y24)).

Interdigital transducer (M_(X1)) and interdigital transducers (R_(X11),R_(X12), R_(X13) and R_(X14)) form four propagation lanes (D_(X11),D_(X12), D_(X13) and D_(X14)) of the surface acoustic wave on the upperend surface of nonpiezoelectric plate (1), respectively. Interdigitaltransducer (M_(X2)) and interdigital transducers (R_(X21), R_(X22),R_(X23) and R_(X24)) form four propagation lanes (D_(X21), D_(X22),D_(X23) and D_(X24)) of the surface acoustic wave on the upper endsurface of nonpiezoelectric plate (1), respectively. Interdigitaltransducer (M_(Y1)) and interdigital transducers (R_(Y11), R_(Y12),R_(Y13) and R_(Y14)) form four propagation lanes (D_(Y11), D_(Y12),D_(Y13) and D_(Y14)) of the surface acoustic wave on the upper endsurface of nonpiezoelectric plate (1), respectively. Interdigitaltransducer (M_(Y2)) and interdigital transducers (R_(Y21), R_(Y22),R_(Y23) and R_(Y24)) form four propagation lanes (D_(Y21), D_(Y22),D_(Y23) and D_(Y24)) of the surface acoustic wave on the upper endsurface of nonpiezoelectric plate (1), respectively. Each of propagationlanes (D_(X11), D_(X12), D_(X13), D_(X14), D_(X21), D_(X22), D_(X23),D_(X24), D_(Y11), D_(Y12), D_(Y13), D_(Y14), D_(Y21), D_(Y22), D_(Y23)and D_(Y24)) consists of minute propagation lanes Z_(j) (j=1, 2, . . . ,X) corresponding to the positions F_(j). Eight propagation lanes(D_(X11), D_(X12), D_(X13), D_(X14), D_(X21), D_(X22), D_(X23) andD_(X24)) and eight propagation lanes (D_(Y11), D_(Y12), D_(Y13),D_(Y14), D_(Y21), D_(Y22), D_(Y23) and D_(Y24)) cross each other. Inaddition, eight propagation lanes (D_(X11), D_(X12), D_(X13), D_(X14),D_(X21), D_(X22), D_(X23) and D_(X24)) are closed each other, and eightpropagation lanes (D_(Y11), D_(Y12), D_(Y13), D_(Y14), D_(Y21), D_(Y22),D_(Y23) and D₂₄) are also closed each other.

When touching a position F_(x), out of the positions F_(j) in FIG. 12,on a minute propagation lane Z_(x) out of the minute propagation lanesZ_(j) of one of the propagation lanes (D_(X11), D_(X12), D_(X13),D_(X14), D_(X21), D_(X22), D_(X23) and D_(X24)), an electric signal Ewith a phase θ is delivered from one of interdigital transducers(R_(X11), R_(X12), R_(X13), R_(X14), R_(X21), R_(X22), R_(X23) andR_(X24)). In this time, only the surface acoustic wave on the minutepropagation lane Z_(x) is disappeared and is not transduced to anelectric signal E_(x) with a phase θ_(x), the electric signal E beingequal to the total electric signal ΣE_(j) minus the electric signalE_(x), the phase θ being equal to the total phase Σθ_(j) minus the phaseθ_(x). Phase comparator (4) detects a difference between the phase θ andthe phase θ_(base), only when the phase comparator (4) is applied withthe electric signal E. Computer (5) finds the position F_(x) from thephase difference (θ_(base) -θ). In the same way, when touching aposition F_(x) on a minute propagation lane Z_(x) out of one of thepropagation lanes (D_(Y11), D_(Y12), D_(Y13), D_(Y14), D_(Y21), D_(Y22),D_(Y23) and D_(Y24)), an electric signal E with a phase θ is deliveredfrom one of interdigital transducers (R_(Y11), R_(Y12), R_(Y13),R_(Y14), R_(Y21), R_(Y22), R_(Y23) and R_(Y24)). In this time, only thesurface acoustic wave on the minute propagation lane Z_(x) isdisappeared and is not transduced to an electric signal E_(x) with aphase θ_(x), the electric signal E being equal to the total electricsignal ΣE_(j) minus the electric signal E_(x), the phase θ being equalto the total phase Σθ_(j) minus the phase θ_(x). Phase comparator (4)detects a difference between the phase θ and the phase θ_(base), onlywhen the phase comparator (4) is applied with the electric signal E.Computer (5) finds the position F_(x) from the phase difference(θ_(base) -θ).

As mentioned previously, switch-change unit (6) under a control ofcomputer (5) in FIG. 14 turns on and off the pair of switches (W₁₁ andW₁₂) and the pair of switches (W₂₁ and W₂₂) alternately. At the sametime, computer (5) detects the pair of switches (W₁₁ and W₁₂) or thepair of switches (W₂₁ and W₂₂) closed when the electric signal E appearsat one of the points Q_(X1), Q_(X2), Q_(X3) and Q_(X4). In the same way,computer (5) detects the pair of switches (W₁₁ and W₁₂) or the pair ofswitches (W₂₁ and W₂₂) closed when the electric signal E appears at thepoint Q_(Y1), Q_(Y2), Q_(Y3) and Q_(Y4). Thus, for example, if the pairof switches (W₂₁ and W₂₂) is closed when the electric signal E appearsat the point Q_(X3), it is clear that the electric signal E is deliveredfrom interdigital transducer (R_(X23)). On the other hand, if the pairof switches (W₁₁ and W₁₂) is closed when the electric signal E appearsat the point Q_(Y1), it is clear that the electric signal E is deliveredfrom interdigital transducer (R_(Y11)). Accordingly, it is clear thatthe touch-position F_(x) exists on a crossing point made by the minutepropagation lane Z_(x) out of the propagation lane (D_(X23)) and theminute propagation lane Z_(x) out of the propagation lane (D_(Y11)).

Compared with the surface acoustic wave position-sensing device in FIG.1, the surface acoustic wave position-sensing device in FIG. 11 can beoperated under still lower power consumption owing to the excitation ofthe unidirectional surface acoustic wave. In addition, no reflection ofa surface acoustic wave generates at the side surface of thepiezoelectric substrate in FIG. 11 because of the excitation of theunidirectional surface acoustic wave. Therefore, the surface acousticwave position-sensing device in FIG. 11 has little or no noise, so thathas a still higher sensitivity.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiment, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A surface acoustic wave position-sensing devicecomprising:two surface acoustic wave transducing units X and Y, eachthereof consisting ofa piezoelectric substrate P_(T) having two endsurfaces running perpendicular to the direction of the thickness dthereof, a piezoelectric substrate P_(R) having two end surfaces runningperpendicular to the direction of the thickness d thereof, an inputinterdigital transducer T_(o) formed on one end surface of saidpiezoelectric substrate P_(T), N input interdigital transducers T_(i)(i=1, 2, . . . , N) formed on said one end surface of said piezoelectricsubstrate P_(T), an output interdigital transducer R_(o) opposed to saidinterdigital transducer T_(o), said interdigital transducer R_(o) beingformed on one end surface of said piezoelectric substrate P_(R) andplaced such that the finger direction of said interdigital transducerR_(o) runs parallel with that of said interdigital transducer T_(o),said thickness d of said piezoelectric substrates P_(T) and P_(R) beingsmaller than an interdigital periodicity P of said interdigitaltransducers T_(o), T_(i) and R_(o), and at least two output interdigitaltransducers R_(i1) and R_(i2) (i=1, 2, . . . , N) opposed to eachinterdigital transducer T_(i), said interdigital transducers R_(i1) andR_(i2) being formed on said one end surface of said piezoelectricsubstrate P_(R) such that the finger direction of said interdigitaltransducers R_(i1) and R_(i2) is slanting to that of said interdigitaltransducer T_(i) by an angle α, respectively, an interdigitalperiodicity P_(N) along the vertical direction to the finger directionof said interdigital transducers R_(i1) and R_(i2) being equal to theproduct of said interdigital periodicity P and cos α; a nonpiezoelectricplate having an upper- and a lower end surfaces running perpendicular tothe thickness direction thereof, the thickness of said nonpiezoelectricplate being larger than three times said interdigital periodicity P,said piezoelectric substrates P_(T) and P_(R) being mounted on saidupper end surface of said nonpiezoelectric plate; and a controllingsystem connected with said surface acoustic wave transducing units X andY,each of said interdigital transducers T_(o) and T_(i) receiving anelectric signal with a frequency approximately corresponding to saidinterdigital periodicity P, exciting a surface acoustic wave of thefirst mode and the higher order modes in said piezoelectric substrateP_(T), and transmitting said surface acoustic wave having the wavelengthapproximately equal to said interdigital periodicity P to saidpiezoelectric substrate P_(R) through said upper end surface of saidnonpiezoelectric plate, the phase velocity of said surface acoustic waveof said first mode and said higher order modes being approximately equalto the phase velocity of the Rayleigh wave traveling on saidnonpiezoelectric plate alone, said interdigital transducer R_(o)transducing said surface acoustic wave excited by said interdigitaltransducer T_(o) to an electric signal with a phase θ_(base) anddelivering said electric signal, each of said interdigital transducersR_(i1) and R_(i2) transducing said surface acoustic wave excited by eachinterdigital transducer T_(i) to electric signals E_(j) (j=1, 2, . . . ,X) with phases θ_(j) (j=1, 2, . . . , X), respectively, said phasesθ_(j) corresponding to positions F_(j) (j=1, 2, . . . , X) on said upperend surface of said nonpiezoelectric plate, respectively, each electricsignal E_(j) having a frequency approximately corresponding to saidinterdigital periodicity P, the total phase Σθ_(j) made by said phasesθ_(j) being zero, the total electric signal ΣE_(j) made by said electricsignals E_(j) being zero and not able to be detected at each of saidinterdigital transducers R_(i1) and R_(i2), said nonpiezoelectric platebeing made of a material such that the phase velocity of the surfaceacoustic wave traveling on said nonpiezoelectric plate alone is higherthan that traveling on said piezoelectric substrates P_(T) and P_(R)alone, said interdigital transducers T_(i) and R_(i1) forming Npropagation lanes D_(i1) (i=1, 2, . . . , N) of the surface acousticwave on said upper end surface of said nonpiezoelectric plate, eachpropagation lane D_(i1) consisting of minute propagation lanes Z_(j)(j=1, 2, . . . , X) corresponding to said positions F_(j), saidinterdigital transducers T_(i) and R_(i2) forming N propagation lanesD_(i2) (i=1, 2, . . . , N) of the surface acoustic wave on said upperend surface of said nonpiezoelectric plate, each propagation lane D_(i2)consisting of minute propagation lanes Z_(j) (j=1, 2, . . . , X)corresponding to said positions F_(j), one of said interdigitaltransducers R_(i1) and R_(i2) delivering an electric signal E with aphase θ only when touching a position F_(x), out of said positionsF_(j), on a minute propagation lane Z_(x) out of said minute propagationlanes Z_(j), said position F_(x) corresponding to an electric signalE_(x) with a phase θ_(x), said total electric signal ΣE_(j) minus saidelectric signal E_(x) being equal to said electric signal E, said totalphase Σθ_(j) minus said phase θ_(x) being equal to said phase θ, saidcontrolling system sensing a touch with a finger or others on saidposition F_(x) by an appearance of said electric signal E at said one ofsaid interdigital transducers R_(i1) and R_(i2), and finding saidposition F_(x) by detecting said one, delivering said electric signal E,of said interdigital transducers R_(i1) and R₁₂, and by evaluating adifference between said phases θ and θ_(base).
 2. A surface acousticwave position-sensing device as defined in claim 1 further comprising:Nswitches W_(i) (i=1, 2, . . . , N) corresponding to said interdigitaltransducers T_(i), an output terminal of each switch W_(i) beingconnected with an input terminal of each interdigital transducerT_(i),output terminals of said interdigital transducers R_(i1) beingconnected with each other at an output point Q₁, output terminals ofsaid interdigital transducers R_(i2) being connected with each other atan output point Q₂, said controlling system turning on and off saidswitches W_(i) with a fixed period in turn, sensing a touch on saidposition F_(x) by an appearance of said electric signal E at one of saidoutput points Q₁ and Q₂, and finding said position F_(x) by detectingsaid one, delivering said electric signal E, of said output points Q₁and Q₂, by choosing a closed one out of said switches W_(i) when saidelectric signal E appears, and by evaluating said difference betweensaid phases θ and θ_(base).
 3. A surface acoustic wave position-sensingdevice as defined in claim 1, wherein the sum of an overlap length L_(P)along the finger direction of said interdigital transducer R_(i1) andthat of said interdigital transducer R_(i2) is approximately equal tothe product of an overlap length L of said interdigital transducer T_(i)and sec α.
 4. A surface acoustic wave position-sensing device as definedin claim 1, wherein two neighbors of said propagation lanes D_(i1) andD_(i2) are closed or partially overlapping each other.
 5. A surfaceacoustic wave position-sensing device as defined in claim 1, whereinsaid propagation lanes D_(i1) and D_(i2) of said surface acoustic wavetransducing unit X and that of said surface acoustic wave transducingunit Y are vertical to each other.
 6. A surface acoustic waveposition-sensing device as defined in claim 1 further comprising:anamplifier A_(x), an input terminal of said interdigital transducer R_(o)of said surface acoustic wave transducing unit X being connected witheach input terminal of said interdigital transducer T_(o) of saidsurface acoustic wave transducing units X and Y via said amplifierA_(x),said interdigital transducers T_(o) and R_(o) in said surfaceacoustic wave transducing unit X, a propagation lane of a surfaceacoustic wave between said interdigital transducers T_(o) and R_(o) insaid surface acoustic wave transducing unit X, and said amplifier A_(x)forming an oscillator.
 7. A surface acoustic wave position-sensingdevice as defined in claim 1, wherein each of said piezoelectricsubstrates P_(T) and P_(R) is made of a piezoelectric ceramic, thepolarization axis thereof being parallel to the thickness directionthereof.
 8. A surface acoustic wave position-sensing device as definedin claim 1, wherein each of said piezoelectric substrates P_(T) andP_(R) is made of a piezoelectric polymer such as PVDF and so on.
 9. Asurface acoustic wave position-sensing device as defined in claim 1further comprising a supporting board cemented to said lower end surfaceof said nonpiezoelectric plate.
 10. A surface acoustic waveposition-sensing device comprising:two surface acoustic wave transducingunits X and Y, each thereof consisting ofa piezoelectric substrate P_(T)having an upper- and a lower end surfaces running perpendicular to thedirection of the thickness d thereof, a piezoelectric substrate P_(R)having an upper- and a lower end surfaces running perpendicular to thedirection of the thickness d thereof, an input interdigital transducerT_(o) formed on said upper end surface of said piezoelectric substrateP_(T), N input interdigital transducers M_(i) (i=1, 2, . . . , N) formedon said upper end surface of said piezoelectric substrate P_(T), eachinterdigital transducer M_(i) consisting of two electrodes M_(i-1) andM_(i-2) and having two kinds of distances between one electrode fingerof said electrode M_(i-1) and two neighboring electrode fingers of saidelectrode M_(i-2), an output interdigital transducer R_(o) opposed tosaid interdigital transducer T_(o), said interdigital transducer R_(o)being formed on said upper end surface of said piezoelectric substrateP_(R) and placed such that the finger direction of said interdigitaltransducer R_(o) runs parallel with that of said interdigital transducerT_(o), said thickness d of said piezoelectric substrates P_(T) and P_(R)being smaller than an interdigital periodicity P of said interdigitaltransducers T_(o), M_(i) and R_(o), at least two output interdigitaltransducers R_(i1) and R_(i2) (i=1, 2, . . . , N) opposed to eachinterdigital transducer M_(i), said interdigital transducers R_(i1) andR_(i2) being formed on said upper end surface of said piezoelectricsubstrate P_(R) such that the finger direction of said interdigitaltransducers R_(i1) and R_(i2) is slanting to that of said interdigitaltransducer M_(i) by an angle α, respectively, an interdigitalperiodicity P_(N) along the vertical direction to the finger directionof said interdigital transducers R_(i1) and R_(i2) being equal to theproduct of said interdigital periodicity P and cos α, N earth electrodesG_(i) (i=1, 2, . . . , N) formed on said lower end surface of saidpiezoelectric substrate P_(T) and corresponding with said interdigitaltransducers M_(i), respectively, and a phase shifter S including atleast a coil L₁ ; a nonpiezoelectric plate having an upper- and a lowerend surfaces running perpendicular to the thickness direction thereof,the thickness of said nonpiezoelectric plate being larger than threetimes said interdigital periodicity P, said piezoelectric substratesP_(T) and P_(R) being mounted on said upper end surface of saidnonpiezoelectric plate through said lower end surfaces of saidpiezoelectric substrates P_(T) and P_(R) ; and a controlling systemconnected with said surface acoustic wave transducing units X and Y,saidinterdigital transducer T_(o) receiving an electric signal with afrequency approximately corresponding to said interdigital periodicityP, exciting a surface acoustic wave of the first mode and the higherorder modes in said piezoelectric substrate P_(T), and transmitting saidsurface acoustic wave having the wavelength approximately equal to saidinterdigital periodicity P to said piezoelectric substrate P_(R) throughsaid upper end surface of said nonpiezoelectric plate, the phasevelocity of said surface acoustic wave of said first mode and saidhigher order modes being approximately equal to the phase velocity ofthe Rayleigh wave traveling on said nonpiezoelectric plate alone, saidinterdigital transducer R_(o) transducing said surface acoustic waveexcited by said interdigital transducer T_(o) to an electric signal witha phase θ_(base) and delivering said electric signal, each interdigitaltransducer M_(i) and each earth electrode G_(i) receiving an electricsignal V₁ with a frequency approximately corresponding to saidinterdigital periodicity P between said electrode M_(i-1) and said earthelectrode G_(i), and another electric signal V₂ with a frequency equalto that of said electric signal V₁ between said electrode M_(i-2) andsaid earth electrode G_(i) via said phase shifter S, exciting anunidirectional surface acoustic wave of the first mode and the higherorder modes in said piezoelectric substrate P_(T), and transmitting saidunidirectional surface acoustic wave having the wavelength approximatelyequal to said interdigital periodicity P to said piezoelectric substrateP_(R) through said upper end surface of said nonpiezoelectric plate, thephase velocity of said surface acoustic wave of said first mode and saidhigher order modes being approximately equal to the phase velocity ofthe Rayleigh wave traveling on said nonpiezoelectric plate alone, thephase difference between said electric signals V₁ and V₂ being 2πy, eachof said interdigital transducers R_(i1) and R_(i2) transducing saidunidirectional surface acoustic wave excited by each interdigitaltransducer M_(i) and each earth electrode G_(i) to electric signalsE_(j) (j=1, 2, . . . , X) with phases θ_(j) (j=1, 2, . . . , X),respectively, said phases θ_(j) corresponding to positions F_(j) (j=1,2, . . . , X) on said upper end surface of said nonpiezoelectric plate,respectively, each electric signal E_(j) having a frequencyapproximately corresponding to said interdigital periodicity P, thetotal phase Σθ_(j) made by said phases θ_(j) being zero, the totalelectric signal ΣE_(j) made by said electric signals E_(j) being zeroand not able to be detected at each of said interdigital transducersR_(i1) and R_(i2), said nonpiezoelectric plate being made of a materialsuch that the phase velocity of the surface acoustic wave traveling onsaid nonpiezoelectric plate alone is higher than that traveling on saidpiezoelectric substrates P_(T) and P_(R) alone, said interdigitaltransducers M_(i) and R_(i1) forming N propagation lanes D_(i1) (i=1, 2,. . . , N) of the surface acoustic wave on said upper end surface ofsaid nonpiezoelectric plate, each propagation lane D_(i1) consisting ofminute propagation lanes Z_(j) (j=1, 2, . . . , X) corresponding to saidpositions F_(j), said interdigital transducers M_(i) and R_(i2) formingN propagation lanes D_(i2) (i=1, 2, . . . , N) of the surface acousticwave on said upper end surface of said nonpiezoelectric plate, eachpropagation lane D_(i2) consisting of minute propagation lanes Z_(j)(j=1, 2, . . . , X) corresponding to said positions F_(j), one of saidinterdigital transducers R_(i1) and R_(i2) delivering an electric signalE with a phase θ only when touching a position F_(x), out of saidpositions F_(j), on a minute propagation lane Z_(x) out of said minutepropagation lanes Z_(j), said position F_(x) corresponding to anelectric signal E_(x) with a phase θ_(x), said total electric signalΣE_(j) minus said electric signal E_(x) being equal to said electricsignal E, said total phase Σθ_(j) minus said phase θ_(x) being equal tosaid phase θ, said controlling system sensing a touch with a finger orothers on said position F_(x) by an appearance of said electric signal Eat said one of said interdigital transducers R_(i1) and R_(i2), andfinding said position F_(x) by detecting said one, delivering saidelectric signal E, of said interdigital transducers R_(i1) and R_(i2),and by evaluating a difference between said phases θ and θ_(base).
 11. Asurface acoustic wave position-sensing device as defined in claim 10further comprising:N pairs of switches W_(i) (i=1, 2, . . . , N)corresponding to said interdigital transducers M_(i), each pair ofswitches W_(i) consisting of two switches W_(i1) and W_(i2), and outputterminals of said switches W_(i1) and W_(i2) being connected with inputterminals of said electrodes M_(i-1) and M_(i-2), respectively,outputterminals of said interdigital transducers R_(i1) being connected witheach other at an output point Q₁, output terminals of said interdigitaltransducers R_(i2) being connected with each other at an output pointQ₂, said controlling system turning on and off said switches W_(i) witha fixed period in turn, sensing a touch on said position F_(x) by anappearance of said electric signal E at one of said output points Q₁ andQ₂, and finding said position F_(x) by detecting said one, deliveringsaid electric signal E, of said output points Q₁ and Q₂, by choosing aclosed one out of said switches W_(i) when said electric signal Eappears, and by evaluating said difference between said phases θ andθ_(base).
 12. A surface acoustic wave position-sensing device as definedin claim 10, wherein x<1/2 in a shorter distance xP of said two kinds ofdistances between one electrode finger of said electrode M_(i-1) and twoneighboring electrode fingers of said electrode M_(i-2), and x+y=±1/2 insaid phase difference 2πy between said electric signals V₁ and V₂.
 13. Asurface acoustic wave position-sensing device as defined in claim 10,wherein the sum of an overlap length L_(P) along the finger direction ofsaid interdigital transducer R_(i1) and that of said interdigitaltransducer R_(i2) is approximately equal to the product of an overlaplength L of said interdigital transducer M_(i) and sec α.
 14. A surfaceacoustic wave position-sensing device as defined in claim 10, whereintwo neighbors of said propagation lanes D_(i1) and D_(i2) are closed orpartially overlapping each other.
 15. A surface acoustic waveposition-sensing device as defined in claim 10, wherein said propagationlanes D_(i1) and D_(i2) of said surface acoustic wave transducing unit Xand that of said surface acoustic wave transducing unit Y are verticalto each other.
 16. A surface acoustic wave position-sensing device asdefined in claim 10 further comprising:an amplifier A_(x), an inputterminal of said interdigital transducer R_(o) of said surface acousticwave transducing unit X being connected with each input terminal of saidinterdigital transducer T_(o) of said surface acoustic wave transducingunits X and Y via said amplifier A_(x),said interdigital transducersT_(o) and R_(o) in said surface acoustic wave transducing unit X, apropagation lane of a surface acoustic wave between said interdigitaltransducers T_(o) and R_(o) in said surface acoustic wave transducingunit X, and said amplifier A_(x) forming an oscillator.
 17. A surfaceacoustic wave position-sensing device as defined in claim 10, whereineach of said piezoelectric substrates P_(T) and P_(R) is made of apiezoelectric ceramic, the polarization axis thereof being parallel tothe thickness direction thereof.
 18. A surface acoustic waveposition-sensing device as defined in claim 10, wherein each of saidpiezoelectric substrates P_(T) and P_(R) is made of a piezoelectricpolymer such as PVDF and so on.
 19. A surface acoustic waveposition-sensing device as defined in claim 10 further comprising asupporting board cemented to said lower end surface of saidnonpiezoelectric plate.